Fatih GÜNDÜZ 030060144 11st Week Bonus Words Answers (Part 3)

Grain boundary sliding : (New) (Better) (Deformation Mechanism)
Grain boundary sliding is well known as the dominant deformation mechanism in conventional microcrystalline materials exhibiting superplasticity (see, e.g., Refs. 57 and 58). Carriers of grain boundary sliding are treated to be grain boundary dislocations with small Burgers vectors being tentatively parallel with grain boundary planes.59 (These small vectors are those of the displacement-shift-complete lattices characterizing grain boundary translational symmetries.)59 In the theory of superplasticity of conventional microcrystal line materials, characteristics of super-plastic How are caused by mechanisms that accommodate grain boundary sliding (see, e.g., Refs. 57 and 58). The same is true in the situation with nanocrystalline materials deformed through grain boundary sliding, in which case, however, the interface and nanoscale effects modify the action of grain boundary sliding and its accommodating mechanisms.
Hahn with workers60,61 have suggested a model describing the grain boundary migration as the accommodation mechanism whose combined action with grain boundary sliding gives rise to plastic flow localization in nanostructured bulk materials and coatings. The model60,61 suggests that grain boundary migration occurs during plastic deformation and results in the formation of a zone where all grain boundary planes are tentatively parallel to each other (Fig. 3.2a,b). The grain boundary sliding is enhanced in this zone which, therefore, develops into a shear band where plastic flow is localized. At the same time, however, the model60,61 does not identify a mechanism for the specific grain boundary migration which makes grain boundary planes to be parallel to each other.
(Nanostructured Coatings, Albano Cavaleiro,J. T. M. De Hosson, p.85)

Grain boundary sliding : (Previous)

Grain boundary sliding a the deformation mechanism that effectively oprates and competes with both the conventional lattice dislocation slip and diffusunonal deformation odes in nanocrystalline materials with the dislocation slip and diffusional deformation modes in nanocrystalline materials with the the fines grains. Grain boundary sliding means a relative shear of neighboring grains that is localized in boundaries between the grains. Comonly grain-boundary sliding occurs in high angle grain boundaries in coarse-grained and nanocrystalline solids .In particular ,the sliding along grain boundaries whit translationally ordered structures can be effectively conducted by movement of sliding grain boundary dislocations.
(Structural nanocrystalline materials: fundamentals and applications ; C. C. Koch; pg 232; First Edition)